1. Field of the Invention
The invention relates to a tape loading mechanism for a magnetic recording/reproducing apparatus such as a video cassette recorder, and more particularly to a structure of a guide groove for guiding a movable tape guide.
2. Description of Related Art
FIG. 1 is a schematic plan view showing a loading state in a video cassette recorder (hereinafter, abbreviated as "VCR"), and FIG. 2 is a schematic plan view showing an unloading state. In the figures, numeral 10 designates a cassette in which a magnetic tape 3 is housed, and which comprises a supply reel 11 for supplying the magnetic tape 3, and a take-up reel 12 for taking up the magnetic tape 3. A rotary drum 1 having video heads 1a and 1b is located in front of the cassette 10. Guide rollers 4a and 4b are disposed at the both sides of the rotary drum 1, respectively. An erase head 5 is disposed between the guide roller 4a and the cassette 10. An audio erase head 6, and an audio signal and control signal head 7 are disposed between the guide roller 4b and the cassette 10. Moreover, a movable pinch roller 8, and a capstan shaft 9 are located in the vicinity of a take-up opening of the cassette 10.
In the loading state, the magnetic tape 3 is wound on the peripheral face of the rotary drum 1 by movable tape guides 3a to 3d. The recording and reproducing processes are conducted under this state. In the unloading state, the magnetic tape 3 is housed in the cassette 10 by the movable tape guides 3a to 3d.
FIG. 3 is a plan view showing a tape loading mechanism of the prior art, and FIG. 4 is a bottom view of the mechanism. The rotary drum 1 is mounted at an adequate position of a main plate 28 which is produced by a die cast process. Guide grooves 23 and 24 along which movable tape guides 21 and 22 slidingly run are formed in the main plate 28 so as to surround the both sides of the rotary drum 1. The movable tape guides 21 and 22 are moved by arm loads 26 and 27 which are rotated and driven by an arm gear load 25.
When the magnetic tape 3 is to be set to the loading state by the movable tape guides 21 and 22, the arm loads 26 and 27 are rotated by the arm gear load 25, so that the movable tape guides 21 and 22 are moved upward in the figure. In this movement, the movable tape guides 21 and 22 travel along the guide grooves 23 and 24. The movable tape guides 21 and 22 are moved each time when a recording or reproducing process is conducted in the VCR, and therefore are required to be structured in a high dimensional accuracy so that they are smoothly moved without rattling. When the magnetic tape 3 is to be wound on the rotary drum 1 by movable tape guides 21 and 22, furthermore, a sufficiently high dimensional accuracy must be attained.
Generally, a die cast process has a feature that a required dimensional accuracy can easily be attained and a higher dimensional accuracy is attained as a thinner die cast product is formed. However, such a die cast process involves a higher cost. When the whole of the main plate 28 is produced by a die cast process, therefore, the cost of a product is increased under the state of the art.
In order to reduce the cost, a countermeasure is taken in which the main plate 28 is made of a metal plate such as an iron plate. However, the drum base portion for supporting the rotary drum 1 must be produced by a die cast process so that a sufficiently high dimensional accuracy is attained. In order to allow the magnetic tape 3 to be accurately wound on the rotary drum 1 in the loading process, furthermore, the guide grooves 23 and 24 which correspond to the positions of the movable tape guides 21 and 22 in the loading process are required to be formed in a part of the drum base portion.
As a result, the guide grooves must be formed, ranging from the main plate made of a metal to the drum base produced by a die cast process. In this case, it produces a problem in that it is very difficult to smoothly move the movable tape guides. FIG. 5 is an enlarged section view showing an example of a joining area of the prior art. In the joining area, a main plate made of a metal, and a drum base produced by a die cast process are joined to each other. In such a structure wherein only a butt joint of the main plate 41 and the drum base 42 is formed, it is impossible to accurately join the drum base 42 to the main plate 41.
In the case where a molding member is formed by using a metal plate in a highly accurate manner, it is general to apply an outsert 41b to the metal plate. Therefore, the thickness of the drum base 42 must coincide with a sum of the thicknesses of the metal plate 41a and the outsert 41b. Accordingly, the thickness of the drum base 42 must be increased so that the feature of the die casting process fails to be sufficiently utilized. This produces another problem in that a high dimensional accuracy cannot be attained.